Honeycomb structural body and canning structural body storing the honeycomb structural body

ABSTRACT

A honeycomb structure according to the present invention has partition walls, and a number of through-holes divided from each other by the partition walls and extending in an axial direction. The honeycomb structure contains silicon carbide (SiC) or a composite material having silicon carbide (SiC) as a main crystal phase, and has a cylindrical shape. A circularity of a periphery of the honeycomb structure is in a range of 1.0 to 2.5 mm. The honeycomb structure can be contained in a metal container in stable state and hardly has problems such as breakage or breakdown.

TECHNICAL FIELD

The present invention relates to a honeycomb structure and a canningstructure containing the honeycomb structure.

BACKGROUND ART

While the recently tightened regulation on exhaust gas has beenimproving in reducing discharged amounts of harmful substances such ashydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NO_(x))from an engine itself; a three-way catalyst, which is the main currentat present, has also been improving. Both of them have been effective inreducing a discharged amount of harmful substances.

However, an amount of harmful substances discharged right after anengine has started is highlightened, while discharged substances arereduced extending over the whole running condition of an engine as theimprovement according to tightening of exhaust gas regulations. Forexample, in FTP-75 cycle, which is a regulated running cycle in U.S.,60-80% of total emission discharged in the whole running cycle isdischarged in the Bag-1 mode for 140 second right after the engine hasstarted. This is because a catalyst is not sufficiently activated sincetemperature of exhaust gas is low right after an engine has started(Bag-1A), thereby passing harmful substances through the catalyst.

Therefore, some measures are employed, for example, putting a catalystas close to an engine as possible in a place where exhaust gas has hightemperature to raise temperature of the catalyst right after an enginehas started, thinning the cell partition walls to decrease heat capacityof a catalyst itself, and increasing cell density of a carrier toquickly absorb heat of exhaust gas and to increase a contact area of acatalyst with exhaust gas.

As a catalyst, there is generally used a catalyst produced by loadingγ-alumina of a fine porous structure having a high surface area on thesurface of cell partition walls of a ceramic honeycomb structure, whichis one of cell structures, and then noble metals such as platinum,palladium, and rhodium are loaded, as catalyst components, on thealumina. Further, to these noble metals are added ceria, zirconia, andthe like, to store and release oxygen contained in exhaust gas. Suchnoble metals and oxygen-storing substances are present in a dispersedstate in the pores in the γ-alumina layer loaded on the surface ofporous cell partition walls (rib) of the carrier.

A honeycomb structure is generally used in such a condition that it ishoused (canned) in a container made of metal such as stainless steelwith being held by the container. In addition, a honeycomb filterobtained by alternately plugging the honeycomb structure at each endface in such a way that it looks checkerboard patterns is suitably usedalso as a filter for capturing and removing particulate matterscontained in dust-containing fluid such as diesel engine exhaust gas(such a filter may hereinbelow be referred to as “DPF.”), and the filteris disposed in a predetermined place after being canned similarly to thecase of the aforementioned honeycomb structure.

Upon canning, an appropriate compressible elastic member is disposed ina gap between the container and a peripheral surface of the honeycombstructure to impart an adequate compressing surface pressure to thehoneycomb structure. An example of related prior art is a method ofcanning a honeycomb structure in a metal container with holding thehoneycomb structure with a mat of an intumescent material containingvermiculite (see U.S. Pat. Nos. 5,207,989 and 5,385,873).

However, in the case of the method disclosed in the above U.S. Pat. Nos.5,207,989 and 5,385,873, compressing surface pressure is rapidly raisedby intumescence. Therefore, the rapidly raised compressing surfacepressure tends to exceed strength (isostatic strength) of a honeycombstructure having thin walls with low strength, and the honeycombstructure is liable to break. In addition, since compressibility of anintumescent mat is quickly deteriorated from about 800 degree C.,compressing surface pressure disappears at about 1000 degree C., and itbecomes impossible to hold the honeycomb structure.

Whereas, in a non-intumescent mat not containing vermiculite (see U.S.Pat. Nos. 5,580,532 and 2,798,871), the change in surface pressureaccording to temperature-rise is very small, and the honeycomb structurecan be held with surface pressure being hardly decreased even at 1000degree C.

A honeycomb structure having thin walls has conventionally been heldusing a non-intumescent mat in place of an intumescent mat. However,when a honeycomb structure is wound with a mat serving as a holdingmember followed by being canned in a metal container, slippage tends tobe caused at the joint of the mat, and surface pressure tends to beincreased. Further, when a honeycomb structure having a mat woundthereon is stuffed in a metal container, the mat tends to have rumples,and surface pressure tends to be increased at that point. These causenon-uniform distribution of compressing surface pressure acting on aperipheral surface of the honeycomb structure. When partially heightenedcompressing surface pressure exceeds isostatic strength of the honeycombstructure, the cell structure breaks. In addition, because of thenon-uniform distribution of the surface pressure, the cell structuretends to slip due to vibrations of an engine or pressure of exhaust gasin practical use.

Incidentally, “isostatic strength” of a honeycomb structure means avalue measured by “isostatic fracture strength test” provided for by theautomobile standards JASO standard M505-87 published by Society ofAutomotive Engineers of Japan, Inc. Specifically, the test is conductedin such a manner that a cell structure as a carrier is put in a rubbertube, and the container is capped and subjected to isotropic pressurecompression, which imitates compression load in the case that a carrieris held at a peripheral surface thereof by a can of a converter. Theisostatic strength is shown by a value of pressure at the time ofbreakage of a carrier. A catalyst converter for purifying automotiveexhaust gas generally employs a canning structure in which a carrier isheld at a peripheral surface thereof. It is a matter of course that highisostatic strength is preferable in view of canning.

When the actual surface pressure becomes higher than the intendedsurface pressure planned upon design of canning, the structure may breakat the point if the surface pressure exceeds isostatic strength of thehoneycomb structure. According as thickness of cell partition wallsdecreases and strength of the structure is lowered, it is necessary todecrease the intended surface pressure, and it is necessary to minimizefluctuation of the surface pressure by suppressing extraordinaryincrease of actual canning surface pressure. It is ideal that the actualsurface pressure is equal to the intended surface pressure because itmakes possible the canning design just as aimed.

Further, a honeycomb structure may break because of varied gap betweenthe honeycomb structure and the metal container due to precision of anexternal shape of the honeycomb structure or because of unevencompression pressure act on the peripheral portion of the honeycombstructure and high holding surface pressure acts partially as a resultof slippage of a holding member caused when the honeycomb structure ishoused in a metal container. As the partition walls of a honeycombstructure are made thinner, the isostatic strength level of thehoneycomb structure becomes lower, which requires to make compressingsurface pressure of the honeycomb structure as low as possible withkeeping the minimum surface pressure required for holding a honeycombstructure. As the level of compressing surface pressure is lowered, itis necessary to make variance in surface pressure smaller, i.e., to givemore uniform distribution of surface pressure.

The present invention has been made in view of the problems of the priorart and aims to provide a honeycomb structure which is capable of beinghoused in a metal container under a safely held condition and whichhardly has problems such as breakage or breakdown, as well as a canningstructure which has a metal container housing the honeycomb structureand which is superior in vibration resistance particularly under hightemperature conditions.

DISCLOSURE OF THE INVENTION

According to the present invention, there is provided a honeycombstructure comprising: partition walls; and a number of through-holesdivided from each other by the partition walls and extending in an axialdirection; the honeycomb structure containing silicon carbide (SiC) or acomposite material having silicon carbide (SiC) as a main crystal phase;and having a cylindrical shape, wherein a circularity of a periphery ofthe honeycomb structure is in a range of 1.0 to 2.5 mm.

According to the present invention, there is also provided a honeycombstructure comprising: partition walls; and a number of through-holesdivided from each other by the partition walls and extending in an axialdirection; the honeycomb structure containing silicon carbide (SiC) or acomposite material containing silicon carbide (SiC) as a main crystalphase; and having a cylindrical shape, wherein a cylindricality of aperiphery of the honeycomb structure is in a range of 1.0 to 3.0 mm.

In the present invention, it is preferable that a second phase of thecomposite material having silicon carbide (SiC) as a main crystal phaseis at least one selected from the group consisting of metallic silicon(Si), metal oxide, metal nitride, metal boride and metal carbide andthat the metal oxide is at least one selected from the group consistingof SiO₂, Al₂O₃ and MgO.

The honeycomb structure is preferably used for purification of exhaustgas of automobile, and more preferably used as a filter for capturingdiesel particulate matter. According to the present invention, there isfurther provided a canning structure comprising: the honeycomb structuredescribed above, and a metal container housing the honeycomb structure;wherein the honeycomb structure is housed in the container in a heldstate by disposing, in a compressed state, a compressible elastic memberhaving thermal resistance and cushioning ability between a peripheralportion of the honeycomb structure and the container.

In the present invention, it is preferable that the metal has acoefficient of thermal expansion of 8×10⁻7 to 13×10⁻⁷ and that the metalis a ferrite-based stainless steel and/or a low thermally-expansiblespecial alloy.

In the present invention, it is preferable that the compressible elasticmember is a ceramic fiber mat and that the ceramic fiber mat is anon-intumescent mat.

Further, in the present invention, it is preferable that a honeycombstructure is housed in the container by any of stuffing, tourniquet,clamshell, swaging, and rotational forging.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partially cut-away view showing one example of the stuffingmethod used for housing a honeycomb structure in a metallic container.

FIG. 2 is a perspective view showing one example of the tourniquetmethod used for housing a honeycomb structure in a metallic container.

FIG. 3 is a perspective view showing one example of the clamshell methodused for housing a honeycomb structure in a metallic container.

FIG. 4 is a sectional view parallel to the direction of through-holes,showing one example of the swaging method used for housing a honeycombstructure in a metallic container.

FIG. 5 is a sectional view parallel to the direction of through-holes,showing one example of the swaging method used for housing a honeycombstructure in a metallic container.

FIG. 6 is a schematic view showing a high-temperature gas generator anda vibration generator connected with the high-temperature gas generator.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the present invention will hereinbelow be described.However, the present invention is by no means limited to theembodiments, and it should be understood that modification in design,improvement, etc., may be adequately performed on the basis of thoseskilled in the art in a range not deviating from the gist of the presentinvention.

The first aspect of the present invention is a honeycomb structurecomprising: partition walls; and a number of through-holes divided fromeach other by the partition walls and extending in an axial direction;the honeycomb structure containing silicon carbide (SiC) or a compositematerial containing silicon carbide (SiC) as a main crystal phase; andhaving a cylindrical shape, wherein a circularity of a periphery of thehoneycomb structure is in a range of 1.0 to 2.5 mm. The details willhereinbelow be described.

As mentioned above, to use a honeycomb structure for purification ofautomotive exhaust gas, it is general to prepare a canning structure byhousing (canning) the honeycomb structure in a container made of metalsuch as stainless steel with being held by the container. A honeycombstructure of the present invention has a circularity of a periphery of1.0 to 2.5 mm. That is, the shape of a section perpendicular to thedirection of through-holes is not exactly circle and the structure,which is cylindrical, has a little distortion. Therefore, when ahoneycomb structure is used in a canning structure, compressing surfacepressure is applied to hold not the whole peripheral surface of thehoneycomb structure, but a partial peripheral surface. A honeycombstructure of the present invention contains silicon carbide (SiC) or acomposite material having silicon carbide (SiC) as a main crystal phase.Its coefficient of thermal expansion is higher in comparison with, forexample, cordierite (silicon carbide: 4×10⁻⁷, cordierite: 0.5×10⁻⁷ to1.2×10⁻⁷) and closer to a coefficient of thermal expansion of a metalconstituting a container (stainless steel: 8×10⁻⁷ to 13×10⁻⁷).

Therefore, it is possible to set lower compressing surface pressure uponcanning a honeycomb structure of the present invention in comparisonwith the case of a honeycomb structure of cordierite. Accordingly, sincea canning structure of the present invention has a structure of applyingthe compressing surface pressure to hold not the whole peripheralsurface but a part of the surface, it is very effective in inhibiting ahoneycomb structure from slipping between the structure and a containeror from falling off from the container due to a temperature differencein a place where the canning structure is placed or in suppressingbreakage of the honeycomb structure due to high compressing surfacepressure as well as it has high vibration resistance under a conditionof high temperature.

Further, to obtain higher effects in inhibiting slippage, falling off,breakage, and the like, it is preferable that the peripheral portion hascircularity of 1.5 to 2.5 mm, more preferably 1.5 to 2.0 mm.Incidentally, “circularity” mentioned in the present invention means avalue indicated by a difference in diameter in a measured section of acylindrical honeycomb structure to show an extent of roundness. Themeasurement is performed by automatic measurement using a lasermeasuring device, digital calipers, or the like.

The second aspect of the present invention is a cylindrical honeycombstructure having partition walls and a number of through-holes dividedfrom each other by the partition walls and extending in an axialdirection, containing silicon carbide (SiC) or a composite materialhaving silicon carbide (SiC) as a main crystal phase, wherein acylindricality of a periphery of the honeycomb structure is in a rangeof 1.0 to 3.0 mm.

In a honeycomb structure of the present invention, a cylindricality ofthe periphery is specified in the rage of 1.0 to 3.0 mm. That is, asection in parallel with the direction of through-holes is not exactlyrectangular and the honeycomb structure, which is cylindrical, has alittle distortion. Therefore, like the first aspect of the presentinvention, i.e., a honeycomb structure whose periphery has a circularityof a predetermined range, compressing surface pressure upon canning isapplied to hold not the whole peripheral surface of the honeycombstructure but a partial peripheral surface in the case that thehoneycomb structure is used in a canning structure.

Since a honeycomb structure of the present invention contains siliconcarbide (SiC) or a composite material having silicon carbide (SiC) as amain crystal phase, it is possible to set lower compressing surfacepressure upon canning a honeycomb structure of the present invention incomparison with the case of a honeycomb structure of cordierite.Accordingly, since a canning structure of the present invention has astructure of applying the compressing surface pressure to hold not thewhole peripheral surface but a part of the surface, it is very effectivein inhibiting a honeycomb structure from slipping between the structureand a container or from falling off from the container due to atemperature difference in a place where the canning structure is placedor in suppressing breakage of the honeycomb structure due to highcompressing surface pressure as well as it has high vibration resistanceunder a condition of high temperature.

Further, to obtain higher effects in inhibiting slippage, falling off,breakage, and the like, it is preferable that the peripheral portion hascylindricality of 1.5 to 2.5 mm. Incidentally, “cylindricality”mentioned in the present invention means a value indicated by adifference in diameters of two coaxial geometrical cylinders (standardcylinders) in the case of forming the minimum gap formed when ahoneycomb structure is sandwiched by the coaxial geometrical cylinders(standard cylinders) to show if its a geometric cylinder or not. Themeasurement is performed by automatic measurement using a lasermeasuring device, digital calipers, or the like, similarly to the caseof measurement for circularity.

For the second phase of the composite material having silicon carbide(SiC) as a main crystal phase, there is preferably used at least oneselected from the group consisting of metallic silicon (Si), metaloxide, metal nitride, metal boride and metal carbide from the viewpointof low thermal expansion, heat resistance, oxidation resistance, and thelike. Specifically, as the above metal oxide, at least one selected fromthe group consisting of SiO₂, Al₂O₃ and MgO is preferably employed inview of practicability. Incidentally, in the present invention, a minutephase inevitably coexist in view of production may be contained besidesthe above main crystal phase and the second phase.

As described above, a honeycomb structure of the present invention ispreferably used as a filter for purifying automotive exhaust gas orfurther for capturing diesel particulate matter by taking advantage offeatures such as high vibration resistance under a condition of hightemperature.

A honeycomb structure of the present invention will hereinbelowdescribed in more detail with an example of a method for productionthereof. In the first place, silicon carbide (SiC) is prepared toproduce a honeycomb structure. Silicon carbide (SiC) sometimes containsminute impurities such as Fe, Al, and Ca. Such silicon carbide may beused as it is or subjected to a chemical treatment such as chemicalwashing to purify. To the silicon carbide (SiC) may be added, as amaterial for forming the second phase, at least one of metallic silicon(Si), metal oxides such as SiO₂, Al₂O₃, and MgO, non-oxides such asmetal nitride, metal boride, and metal carbide, and the like.

For smooth extrusion of clay into a honeycomb shape, it is preferablethat at least one suitable organic binder is added in an appropriateamount. Further, water and the like are added to the material, followedby mixing and kneading to obtain clay for forming.

When partition walls (cell partition walls) constituting cells of thehoneycomb structure are used as a filter, a pore former is added to thematerial for preparing clay to raise the porosity. In this case, sincepores are formed at the space where the pore former disappears after theburning, it is preferable to use a pore former having the averageparticle diameter within the range from 100 to 150% with respect to theintended average pore diameter after being fired.

The clay obtained by mixing and kneading the above material by anordinary method is formed into a honeycomb structure having a desiredcell shape by extrusion or the like. As to a cell shape, it is generalthat a honeycomb structure used as a DPF has a square cell shape.However, in a honeycomb structure of the present invention, a cell shapeis not restricted to a square and may be a rectangle, a triangle, ahexagon, a circle, or the like.

When a honeycomb structure is used as a catalyst carrier forpurification of automotive exhaust gas or as a DPF, the cell partitionwalls may have a thickness of 0.11 to 0.17 mm, and a cell density may be300 to 1200 cpsi, or the cell partition walls may have a lower thicknessof 0.02 to 0.10 mm. A honeycomb structure used for a heat-exchanger mayhave a structure having a high cell density of 1200 cpsi or more.Incidentally, a cell structure is specified by a cell wall thickness anda cell density, and a cell density is generally shown by cpsi. Forexample, a cell density of 400 cpsi means presence of 400 cells persquare inch, and “cpsi” is an abbreviation of “cells per square inch”.Cell partition wall thickness is also called as rib thickness, and ithas conventionally shown with a unit “mil”. One mil is 1×10⁻³ inch, andit is about 0.025 mm.

The formed body obtained above is calcined to remove an organic bindercontained in the formed body, and then subjected to firing. It ispreferable that the calcination is performed at a temperature lower thana temperature at which metallic silicon melts. Specifically, it maytemporarily be kept at a predetermined temperature of about 150 to 700degree C. Alternatively, calcination may be conducted at a heating rateof 50 degree C./hr or less within the predetermined temperature range.

In the manner of temporarily keeping the formed body at a predeterminedtemperature, the formed body may be kept at one temperature level or atplural temperature levels. When the formed body is kept at pluraltemperature levels, the time for keeping the temperature may be the sameor different from each other. Similarly, as to a manner of making slowera heating rate, the heating rate may be made slower in a certaintemperature range or in plural temperature ranges. When the heating rateis made slower in plural ranges, the rate may be the same or differentfrom each other.

The calcination may be performed in an oxidization atmosphere. However,in the case that a large amount of organic binder(s) is contained in theformed body, the organic binder(s) sometimes burn(s) furiously withoxygen to raise temperature of the formed body rapidly during thecalcination. Therefore, in such a case, it is also preferable to performthe calcination in an inert atmosphere such as N₂ and Ar to suppressextraordinary temperature rise of the formed body.

The calcination and the following main firing may be performed in thesame furnace or different furnaces as different steps. Alternatively,they may be performed in the same furnace as successive steps. Theformer manner is also preferable when the calcination and the mainfiring are performed in different atmospheres. However, the lattermanner is also preferable from the viewpoint of total firing time,running cost of a furnace, and the like.

The optimum firing temperature during the main firing is determineddepending on a micro-structure and properties, and the temperature of1400 to 1800 degree C. is appropriate in general. As to an atmosphere ofthe main firing, a non-oxidizing atmosphere such as N₂ and Ar ispreferable to avoid oxidation of silicon carbide at high temperature.

When the honeycomb structure of the present invention is used as acarrier for catalyst in an internal combustion engine, a boiler, achemical reactor, a fuel cell reformer, or the like, the honeycombsegments used therein are allowed to load thereon a metal having acatalytic activity. As representative metals having a catalyticactivity, there are mentioned Pt, Pd, Rh, K, Na, Li, etc. It ispreferred that at least one selected from these metals is loaded on thehoneycomb segments.

On the other hand, when the honeycomb structure of the present inventionis used as a filter for capturing particulate matter in exhaust gas suchas DPF, cell walls are made to a filter by plugging cells alternately ateach end face so that the end faces show checkerboard pattern. Whenexhaust gas containing particulate matter is taken into a honeycombstructure constituted by such honeycomb segments, from its one end face,the exhaust gas enters the inside of the honeycomb structure from thoseopenings not plugged at the one end face, passes through porous cellwalls having a filtration ability, and is discharged from the openingsnot plugged at the other end. When the exhaust gas passes through thecell walls, the particulate matter present in the exhaust gas iscaptured by the partition walls.

As the captured particulate matter builds up on cell walls, pressureloss increases rapidly, an engine load increases, fuel consumption anddrivability deteriorate; hence, the particulate matter is burnt andremoved periodically by a heating means such as a heater, to regenerateability of the filter. In order to promote the combustion during theregeneration, metal having a catalytic activity such as mentioned abovemay be loaded on the honeycomb structure.

Next, description is made on the third aspect of the present invention.The third aspect of the present invention is a canning structurecomprising: any of the honeycomb structure mentioned above, and a metalcontainer housing the honeycomb structure; wherein the honeycombstructure is housed in the container in a held state by disposing, in acompressed state, a compressible elastic member having thermalresistance and cushioning ability between a peripheral portion of thehoneycomb structure and the container. The details will hereinbelow bedescribed.

As described above, since a peripheral portion of a honeycomb structureof the present invention has a predetermined circularity orcylindricality, a canning structure of the present invention obtained byusing the honeycomb structure of the present invention hold not thewhole peripheral surface of the honeycomb structure but a part of theperipheral surface by compressing surface pressure applied when thehoneycomb structure is canned with a compressible heat-insulatingmaterial being disposed between a peripheral portion of the honeycombstructure and a metal container. Since the honeycomb structure to behoused in the container is constituted by silicon carbide (SiC), thestructure has a coefficient of thermal expansion higher than that ofcordierite (silicon carbide: 4×10⁻⁷, cordierite: 0.5×10⁻⁷ to 1.2×10⁻⁷)and the coefficient of thermal expansion is close to that of the metalconstituting the container (stainless steel: about 10×10⁻⁷).

Therefore, as to a canning structure of the present invention, it ispossible to set lower compressing surface pressure upon canning ahoneycomb structure of the present invention in comparison with the caseof a honeycomb structure of cordierite. Accordingly, since a canningstructure of the present invention has a structure of applying thecompressing surface pressure to hold not the whole peripheral surfacebut a part of the surface, it is very effective in inhibiting ahoneycomb structure from slipping between the structure and a containeror from falling off from the container due to a temperature differencein a place where the canning structure is placed or in suppressingbreakage of the honeycomb structure due to high compressing surfacepressure as well as it has high vibration resistance under a conditionof high temperature.

Further, it is preferable that the metal constituting the container forhousing the honeycomb structure has a coefficient of thermal expansionof 8×10⁻7 to 13×10⁻⁷, more preferably 8×10⁻⁷ to 1×10⁻⁷. A canningstructure with a container of a metal having a coefficient of thermalexpansion within the above range shows superior characteristics such asvibration resistance under a condition of high temperature from therelation among a coefficient of thermal expansion of 4×10⁻⁷ of siliconcarbide (SiC) constituting the honeycomb structure, circularity, andcylindricality.

In addition, it is preferable that the metal constituting the containerfor housing the honeycomb structure is a ferrite-based stainless steeland/or a low thermally-expansible special alloy. Each of these metalshas a coefficient of thermal expansion suitable for constituting acontainer of a canning structure showing superior characteristics suchas vibration resistance under a condition of high temperature from therelation among a coefficient of thermal expansion of silicon carbide(SiC) constituting a honeycomb structure, circularity and cylindricalityof a peripheral portion of the honeycomb structure.

In the present invention, it is preferable that the compressible elasticmember is a ceramic fiber mat. This is because a ceramic fiber mat hassufficient heat resistance and cushioning ability as well as it caneasily be obtained and processed. A preferable ceramic fiber mat is anon-intumescent mat substantially not containing vermiculite, alow-intumescent mat containing a small amount of vermiculite, or thelike, and contains as the main component, ceramic fibers comprisingalumina, high-alumina, mullite, silicon carbide, silicon nitride,zirconia, titania, or a mixture thereof. Among these, further preferableis a non-intumescent mat substantially not containing vermiculite andcontaining, as the main component, alumina or mullite.

Next, a canning structure of the present invention is hereinbelowdescribed in more detail with an example of a method for productionthereof. A canning structure can be obtained by housing, in a metalcontainer, a honeycomb structure of the present invention obtained inthe aforementioned method of production. In the present invention, thepreferable methods to impart compressing surface pressure to thehoneycomb structure by means of housing of the honeycomb structure inthe container and a compressible elastic member is as follows.

That is, there are suitably used a stuffing method shown in FIG. 1,using a guide 17; a tourniquet method shown in FIG. 2, which compriseswinding a metallic plate 11 c around a honeycomb structure, pulling theplate to impart a pressure to the outer surface of the honeycombstructure, and welding and fixing the to-be-jointed areas of themetallic plate 11 c; and a clamshell method shown in FIG. 3, whichcomprises interposing a honeycomb structure between two metalliccontainer parts 11 a and 11 b with applying a load to the parts 11 a and11 b, and welding the to-be-bonded areas (flanges) 16 a and 16 b of theparts 11 a and 11 b to obtain a bonded container. There is also suitablyused a swaging method utilizing metal forming technology, shown in FIG.4, which comprises applying a compression force to a metallic container11 from the outside via a tap (of pressure type) to reduce the outerdiameter of the metallic container 11. Further, there can also besuitably used a swaging method as shown in FIG. 5, which comprisesspinning the outer surface of a metallic container 11 by metal formingprocess using a processing jig 18 with the metallic container 11 beingrotated, to reduce the outer diameter of a metallic container, andthereby imparting a pressure to the outer surface of a honeycombstructure in the metallic container. Incidentally, in FIG. 1, thereference numeral 1 denotes a honeycomb structure, the reference numeral5 denotes a compressible elastic body B, and the reference numeral 11denotes a metal container. Even in the other drawings, the samereference numerals denote the same portions.

The concrete results of the present invention performed are hereinbelowdescribed.

EXAMPLES 1 TO 33, COMPARATIVE EXAMPLES 1 TO 14

A silicon carbide powder was used as a raw material. Thereto were addedmethyl cellulose, hydroxypropoxylmethyl cellulose, a surfactant andwater to prepare clay having plasticity. The clay was subjected toextrusion to give a honeycomb shape, followed by drying, and then bothend faces were alternately plugged with a plugging material of the samematerial as the honeycomb structure so that the end faces showcheckerboard pattern. After heat-degreasing the honeycomb shaped clay ina N₂ atmosphere, it was fired in an Ar atmosphere to obtain acylindrical honeycomb structure having a diameter of 5.66 inches, alength of 6 inches, and a thickness of 15 mil/cell density of 300 cpi.Incidentally, each of the honeycomb structures obtained was measured forporosity and average pore diameter using a mercury porosimeter, and forcircularity and cylindricality by the method described above. Theresults are shown in Tables 1 and 2.

A ceramic non-expansible mat having a thickness of 6.8 mm is woundaround the peripheral portion of each of the honeycomb structuresobtained above, and each of the honeycomb structures was pressed in aSUS409 can for canning to obtain a canning structure. Incidentally, theceramic non-intumescent mat had a thickness of 4 mm after being pressedin the can.

(Evaluation of Durability)

A canning structure was evaluated for durability using ahigh-temperature gas generator 23 shown in FIG. 6 and a vibrationgenerator 21 connected with the high-temperature gas generator 23. Afterthe canning structure 20 was set at the vibrating portion 22 of thevibration generator 21, a high-temperature gas generated from thehigh-temperature gas generator 23 was sent in the honeycomb structurefrom the lower end face (exhaust gas flow-in end face) and dischargedfrom the upper end face (exhaust gas flow-out end face), with operatingthe vibration generator 21 to generate vertical vibrations.Incidentally, the durability test time was 100 hours, the temperature ofthe high-temperature gas was 700 degree C., and the vibrations appliedwas 100 Hz at 60 G. After the durability test time passed, the canningstructure was taken out, and conditions of the honeycomb structure wereevaluated. The results are shown in Tables 1 and 2. Incidentally, theevaluations of the durability were given with “bad” in the case thatboth slipping and breakage of the honeycomb structure were caused,“fair” in the case that breakage of the honeycomb structure was caused,“good” in the case of a honeycomb structure with a little slipping (1 mmor less), and “excellent” in the case of the honeycomb structure havingno problem. Incidentally, in FIG. 6, the reference numeral 30 denotes anexhaust port, the reference numeral 31 denotes a flowmeter, and thereference numeral 32 denotes a burner. TABLE 1 Porosity Average poreCircularity (%) diameter (μm) (mm) Durability Example 1 38 10 2Excellent Example 2 44 14 2 Excellent Example 3 47 20 2 ExcellentExample 4 38 11 1.5 Excellent Example 5 44 15 1.5 Excellent Example 6 4720 1.5 Excellent Example 7 38 11 2.5 Good Example 8 44 14 2.5 ExcellentExample 9 47 20 2.5 Excellent Example 10 38 9 1 Good Example 11 47 20 1Excellent Example 12 44 16 1 Excellent Example 13 58 25 2.5 Good Example14 58 26 2 Excellent Example 15 58 25 1.5 Excellent Example 16 58 24 1Excellent Comp. Ex. 1 38 10 0.5 Bad Comp. Ex. 2 44 16 0.5 Bad Comp. Ex.3 47 21 0.5 Fair Comp. Ex. 4 38 10 3 Fair Comp. Ex. 5 44 16 3 Bad Comp.Ex. 6 47 19 3 Bad

TABLE 2 Porosity Average pore Cylindricality (%) diameter (μm) (mm)Durability Example 17 38 10 2 Excellent Example 18 44 16 2 ExcellentExample 19 47 19 2 Excellent Example 20 38 11 1.5 Excellent Example 2144 16 1.5 Excellent Example 22 47 21 1.5 Excellent Example 23 38 11 2.5Excellent Example 24 44 15 2.5 Excellent Example 25 47 20 2.5 ExcellentExample 26 58 26 2.5 Excellent Example 27 58 25 1 Good Example 28 58 251.5 Excellent Example 29 58 24 2 Excellent Example 30 58 24 3 ExcellentExample 31 38 11 3 Good Example 32 47 19 3 Excellent Example 33 44 16 3Excellent Comp. Ex. 7 38 11 0.5 Bad Comp. Ex. 8 44 16 0.5 Bad Comp. Ex.9 47 20 0.5 Bad Comp. Ex. 10 38 9 3.5 Fair Comp. Ex. 11 44 15 3.5 FairComp. Ex. 12 47 21 3.5 Fair Comp. Ex. 13 58 26 0.5 Fair Comp. Ex. 14 5825 3.5 Bad

As obvious from the results shown in Tables 1 and 2, with regard tocanning structures each showing a circularity within the range from 1.0to 2.5 mm in Examples 1 to 16 and canning structures each showing acylindricality within the range from 1.0 to 3.0 mm in Examples 17 to 33,no problem such as slipping or breakage of the honeycomb structure wascaused, and this made clear that these canning structures shows superiorhigh-temperature vibration resistance to the canning structures eachcanned with a similar compressing surface pressure in ComparativeExamples 1 to 14.

INDUSTRIAL APPLICABILITY

As described above, since a honeycomb structure of the present inventionhas a predetermined circularity and cylindricality, it can be housed ina metal container under a safely held condition and hardly has problemssuch as breakage or break down. In addition, since a canning structureof the present invention has a metal container housing the abovehoneycomb structure, it is superior in vibration resistance particularlyunder high temperature conditions.

1-12. (canceled)
 13. A honeycomb structure comprising: partition walls;and a number of through-holes divided from each other by the partitionwalls and extending in an axial direction; the honeycomb structurecontaining silicon carbide (SiC) or a composite material having siliconcarbide (SiC) as a main crystal phase; and having a cylindrical shape;wherein a circularity of a periphery of the honeycomb structure is in arange of 1.0 to 2.5 mm, or a cylindricality of a periphery of thehoneycomb structure is in a range of 1.0 to 3.0 mm.
 14. The honeycombstructure according to claim 13, wherein a second phase of the compositematerial having silicon carbide (SiC) as a main crystal phase is atleast one selected from the group consisting of metallic silicon (Si),metal oxide, metal nitride, metal boride and metal carbide.
 15. Thehoneycomb structure according to claim 14, wherein the metal oxide is atleast one selected from the group consisting of SiO₂, Al₂O₃ and MgO. 16.The honeycomb structure according to claim 13, wherein the honeycombstructure is used for purifying automotive exhaust gas.
 17. Thehoneycomb structure according to any of claim 13, wherein the honeycombstructure is used as a diesel particulate filter.
 18. A canningstructure comprising: a honeycomb structure; and a metal containerhousing the honeycomb structure; wherein the honeycomb structure ishoused in the container in a held state by disposing, in a compressedstate, a compressible elastic member having thermal resistance andcushioning ability between a peripheral portion of the honeycombstructure and the container; the honeycomb structure comprising:partition walls; and a number of through-holes divided from each otherby the partition walls and extending in an axial direction; thehoneycomb structure containing silicon carbide (SiC) or a compositematerial having silicon carbide (SiC) as a main crystal phase; andhaving a cylindrical shape; a circularity of a periphery of thehoneycomb structure being in a range of 1.0 to 2.5 mm, or acylindricality of a periphery of the honeycomb structure being in arange of 1.0 to 3.0 mm.
 19. The canning structure according to claim 18,wherein the metal has a coefficient of thermal expansion of 8×10⁻⁷ to13×10⁻⁷.
 20. The canning structure according to claim 18, wherein themetal is a ferrite-based stainless steel and/or a lowthermally-expansible special alloy.
 21. The canning structure accordingto claim 18, wherein the compressible elastic member is a ceramic fibermat.
 22. The canning structure according to claim 21, wherein theceramic fiber mat is a non-intumescent mat.
 23. The canning structureaccording to claim 18, wherein the honeycomb structure is housed in thecontainer by stuffing, tourniquet, clamshell, swaging, and rotationalforging.